Hello Friends

to continue
Lambda repressor is under tight regulation.
Two types of regulation
1. Positive Autoregulation
2.Negative Autoregulation

1. Positive Autoregulation:
It activates its own expression.
It makes level do not reach so low.

2.Negative Autoregulation:
PRM being activated by repressor at OR2 to make more repressor but if concentration increases too high repressor will bind to OR3 also and repress PRM.
This act decreases concentration of repressor.

On new infection the phage has to chose between lytic and lysogeny.
cII and cIII products decide this step.
cII transcribed from PR and cIII from PL.
cII is transcriptional activator it binds to a site called PRE(Repressor Establishment)
PRE stimulate transcription of cI(repressor).
Thus, repressor can be transcribed from PRE and PRM.
PRE is weak promoter so cII product help polymerase bind to PRE.
Once, sufficient repressors are made from PRE, they can bind to OR1 and OR2 and directs their own synthesis from PRM.
Thus repressor synthesis established from one promoter and maintained by other promoter.
Thus, upon infection transcription immediately initiate from PR and PL.
PR synthesise both cro and cII.
cro favours lytic phase. Once cro product is at certain level of concentration it will bind OR3 and block PRM activity.
cII favours lysogeny by directing transcription of repressor gene and for successful lysogeny repressor must bind to OR1 and OR2 and activate PRM before cro inhibit that promoter.
So, phage favous lytic in good bacterial growth environment and lysogeny in poor conditions.

For diagrams you can consult books or diagrams online.

Hope this will help you all. See you all in next blog.
Thnkyou for reading.